Electroforming apparatus



Sept. l2, H950 E. G. CAMERON ETAL 2,521,687

ELECTROFORMING APPARATUS 2 Sheets-Sheet 1 Filed July 25, 1947 nulliE A.C. SOURCE BY y ym'Traum? Sept 12, 1950 E. G. CAMERON ETAL 2,521,687

ELECTROFORMING APPARATUS lli-M;

\ 'HMP Miss! l www wwwMM5 Z5 5a 55 5a 39 e4 BY /f/ ATTORNEY Patented Sept. l2, 1950 UNITED STATES PATENT OFFICE ELECTROFORMING APPARATUS Application July 23, 1947, Serial No. 762,974

7 Claims.

This invention relates to the art of electroforming electrical elements such as rectifers and photocells of the plate type and more particularly to apparatus to facilitate the electroforming operation.

The invention has particular application to the electroforming of dry-plate or metallic rectifiers, such as selenium rectifiers, customarily composed of electrode plates of steel or aluminum, which may or may not be plated -with nickel or the like, to which is adherently applied a coating of semi-conductive material, such as selenium, and over which is applied a. counterelectrode of a suitable alloy, such as Woods metal. Such rectifier elements are commonly electroformed before used, so as to be operable -with maximum efficiency, by applying to them a voltage to send the current through the rectifier element in the direction opposite to the direction of normal forward current flow. By application of the voltage in the relation referred to, rectifying properties are produced which are believed due to the formation of a barrier layer at the selenium surface underlying the counterelectrode layer.

One of the objects of this invention is to provide apparatus for electroforming a plurality of rectifier elements in a cooling medium, such as oil for example.

Another object of the invention is to provide a device in which a plurality of rectifier elements may be quickly assembled for support during the electroforming operation and which can be quickly removed therefrom when the electroforming operation has been completed.

In accordance with one feature of the invention, a tank is provided with electrical terminals to which devices supporting one or more rectifier elements may be connected for submersion in a cooling medium such as oil contained in the tank. Associated with the tank is a heat exchange unit, a filter and a pump, whereby the medium may be circulated for cleaning and temperature control. Also associated with the tank in connection with certain of the electrical terminals are ballast resistors having a. characteristic such that, as the resistance of the rectifier elements increases during electroforming, the resistance of the ballast decreases proportionally. This provides for automatic voltage regulation during electroforming.

A further feature of the invention is the construction of the device which supports rectifier elements for submersion in the cooling medium. The device includes a plurality of conductor strips arranged in overlapping relation between which rectifier elements may be easily and quickly positioned, the device being provided with means for clamping the rectifier elements thus positioned between the strips'. Alternate strips are preferably connected in circuit whereby the rectifier elements may be disposed in pairs in opposite direction such as back-to-back for application of alternating current.

Another feature of the invention is the shaping of the conductor strips with areas projecting from the plane thereof for engagement with the rectifier elements, whereby spaces are provided between each strip and the adjacent rectifier for circulation of the cooling medium. In addition to the circulating feature, the strips act not only as spacer elements but as additional heat conducting fins for the rectifiers.

The above and other objects and features of the invention will be more fully understood by reference to the accompanying drawings, in which:

Fig. 1 is a diagrammatical view in plan of ap.

ratus there shown comprises a tank I provided with an input connection 2 and an output connection 3 for the circulation of a coolingmedium of insulating quality, such for example as transformer oil. The outlet connection 3 delivers the oil to a heat exchange unit I for temperature control and the dissipation of heat generated by the rectifier elements during the electroforming operation. The unit 4 is provided with a cool-y ing coil 5 through which a cooling fiuid, such as water, is circulated. The oil is passed from the heat exchange unit 4 through a filter 6 to remove foreign particles and is then delivered by pump l through inlet connection 2 to a distributor pipe 8. Y

The tank is further provided with a terminal 9 at the bottom of the tank at one side thereof and a series of small terminals I0, Il, I2 and I3 at the opposite side of the tank. Terminals Il! to I3 are connected to ballast resistors Il. I5, I6 and I1, respectively and thence to one side I8 of a source of alternating current, the other side I l of which is connected to the terminal l. Connected across the terminal I and each of the series of terminals Il to Il are rectifier supporting devices 2l, as indicated in broken lines in Fig. l. By supporting a large number of rectifier elements in each device and providing a number of such devices submerged in the tank, it is possible to electroform a large number of rectifier elements simultaneously.

In Figs. 2, 3 and 4, one oi the rectier supporting devices is shown in detail. The device comprises two end plates 2| and 2! which are provided with spring clamps 23 and 2l at the lower ends thereof for clamping engagement, respectively, with terminal I ,and one oi' the terminals Il to It. The two end plates are connected together by two pairs of tie rods Il. 2l and 21, 2l, the tie rods being arranged at the corners of a rectangle with each pair comprising the tie rods disposed at the corners cross-wise of the rectangle, cach tie rod being provided with an insulating sleeve 2|. Supported on the insulated sleeves of each pair of tie rods I5, 2l are two groups of conductor strips Il and 3|, the strips of the two groups being arranged alternately as shown in Fig. 2. Two groups of conductor strips $2 and are similarly supported on the insulating sleeves of rods 21 and 2l. The strips on each rod are separated by insulating washers 84. The strips on one pair of tie rods are alternated with Athe strips on the other pair of tie rods in crisscross relation, as indicated in Fig. 4. This crisscross relationship is particularly desirable since it facilitates greatly the assembling of rectifier elements between adjacent strips. The rectiiier elements are placed one between each adjacent pair of strips in a location such as indicated in broken lines I5, Fig. 4, the rectifier elements being disposed in pairs and back-to-back" for application of alternating current.

The electrical circuit is connected only to the strips on one of the pairs of tie rods. For example, the electric circuit is connected by lead 30 from the spring clamp 23 to the iirst strip $3. as viewed in Fig. 3. All of the strips I3 are connected together by ilexible conductor cable l1. The strips 32 are similarly connected together by a ilexible cable 38 adjacent the opposite tie rod 2l, the strips I2 being connected by lead l! to the spring clamp 24. It will be observed that disposed between the strips $2 and Il is a strip Il or 3|, as the case may be. The strips 30 and Ii may be regarded as neutral, the rectiilers being interposed between a live strip l! or Il and one of the neutral strips Il or 3i so that the current passing through the rectiners passes from one oi the live strips through a rectifier to a neutral strip and then from a neutral strip through the next rectifier to the live strip on the other side of the circuit. While the rectiner may be positioned so as to face a given direction i'or application of direct current, we prefer to place the rectiers so that they face in opposite directions for application of alternating current.

While the strips I0, 3i, 32 and Il may be diiferent, that is certain of them may be plane and others provided with projections, we prefer to make them identical. Each strip, for example, is especially formed so as to provide projecting areas from the plane of the strip for contact with the adjacent rectiiier element. The projections are disposed in three groups, the center group of projections Il, Il are trapeaoidal in shape and are pressed alternately in opposite directions with respect to the plane of the strip, as shown in 4 Figs. 5 and 6. The second and third groups are in the form of detents 42 and 4I located above and below the center projections 4t, 4i, alternate detents being disposed in opposite directions as indicated in Fig. 6. The projections 4l, 4i provide for both heat and electrical conduction and also furnish spaces between the strip and the adjacent rectiers for the circulation of the cooling liquid. 'I'he detents l2 and I3 assist in the proper positioning of the rectiilers, the detents iaeing slightly lower than the projections 4I and The end plate 22 is provided with an abutment M while end plate 2| is provided with a thumb screw I5 in alignment with the abutment, so that when screw Il is adjusted to engage an end plate 46 carried on tie rods 2l and 2t the conductor strips and the rectifier elements disposed therebetween may be clamped together. The device 2l when loaded with rectiiler elements between the conductor strips and clamped sothatthey cannot be dislodged, is ready for the electroiorming tank. The end plates are provided with handles or openings 41 for easy manipulation, the operator being thereby able to immerse the main portion of the device including the conductor strips in the oil bath with the conductor clamps 2J and 24 engaging terminal l and one oi the individual terminals, such as terminal Il. Thus submerged. the electroforming operation may proceed, the ballast resistor Il connected in series therewith providing a relatively high resistance during the initial period of the electroforming operation. As the electroiorming proceeds thereby developing in the rectifier a high resistance to reverse current tiow, thus reducing the current in ballast Il, the resistance of the ballast i4 in turn decreases thereby producing an increase in the voltage across the rectiilers. A suitable ballast for this purpose may comprise one or more incandescent lamps, the resistance oi which decreases with decrease in current.

When the rectiers have been suiiiciently electroiormed, the device 2l may be liited from the tank. By retracting the thumb screw 4I, the

clamping pressure on the rectiiiers and conductor strips is released, and the rectiner elements may then be easily dislodged. Before the rectiiiers are removed from the device any indication of shorts may be checked by applying the terminals oi a meter across adjacent strips, that is, a live strip such as strips l2 and l! and a neutral strip such as lll and Il. The rectiiiers may be similarly graded while they are in the device 2l. While one embodiment of the invention has been disclosed, it will be clear to those skilled in the art that many variations and modiiications of the tank arrangement and the rectifier supporting device 2l are possible without departing from the invention. For example, the electrical terminals for the tank may be dliierently arranged and a different electrical connection may be provided for the device 2l. Also, the arrangement and shape o! the conductor strips and the projections thereon may be considerably varied without departing from the intended Purpe thereof. It is to be understood, therefore, that the present disclosure is to be regarded as illustrative of the invention only and not as a limitation of the scope thereof.

We claim:

1. An apparatus for electroforming rectiners comprising a tank of insulating liquid, spaced electric terminals in said tank, and a device to support rectiiier elements for immersion in aid tank, said device comprising a pair of end plates, tie rods connecting said end plates, a plurality of conductor strips carried by said tie rods, means to apply clamping pressure to said strips to clamp rectiiler elements therebetween, a pair of connectors carried by said end plates for connection with said terminals, and means connecting one of said connectors to certain of said strips and the other connector to certain other of said strips.

2. Apparatus according to claim 1, wherein each of said strips has areas projecting outwardly from the plane of the strip ior engagement with rectiiler elements disposed between adjacent strips whereby spaces are provided between said strips and therectifier elements for circulation of said liquid.

3. Apparatus according to claim 1, further including a liquid cooling chamber, a lter' and means for causing circulation of said insulating liquid through said tank, said chamber and said lter.

4. Apparatus according to claim 1, further including a plurality of such devices to support rectiiier elements for immersion in said tank, each such device having rone individual terminal and a ballast connected thereto, said ballast having the characteristic as the resistance of the rectliler elements increases the resistance of the ballast decreases.

5. In apparatus for electroforming selenium rectiiier elements, a, support for a plurality of said elements comprising a plurality of parallel rods, a plurality of sets of conductor strips extending transversely from respective ones of said rods, the strips of different sets being interleaved with one another, whereby a plurality of rectitler elements may be inserted between respective pairs of said strips so that each element is in contact with two strips belonging to dinerent sets, a source oi current, conductor means connecting the strips of certain o! said sets in parallel to said source, and circuit means including said source, said conductor means and said strips for passing a forming current through the elements thus inserted.

6. In apparatus for electroforming selenium rectifier elements, a support according to claim 5, further comprising clamping means for clamping said strips and rectier elements together after said elements have been inserted.

7. In apparatus for electroforming selenium rectiiier elements. a. support according to claim 6 comprising a pair of end plates secured to said rods at opposite ends thereof, said clamping means comprising a movable plate slidably mounted on said rods between one of said end plates and the nearest strip, and screw means for displacing said movable plate relative to said one end plate.

EMMET G. CAMERON. HAROLD A. KEIPER. AUGUST D. MI'ISCHKE. LESLIE G. BURLINGAME. ROBERT W. FERGUSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 830,924 Pawlowski Sept. 11, 1906 2,239,770 Becker Apr. 29, 1941 2,279,187 Thompson et al Apr. 7,. 1942 2,348,311 Ruben May 9, 1944 2,368,749 Dowling et al Feb. 6, 1945 2,390,771 Blackburn Dec. 11, 1945 2,444,255 Hewlett June 29, 1948 FOREIGN PATENTS Number Country Date 318,265 Great Britain Dec. l, 1930 

